Replacing values in an array over a certain value

I am currently writing a piece of software that will calculate solar radiation on a vertical plane. I currently have a 1x49 array, containing values for my incident angle, however some of these values are greater than 90, and i wish to minus 180 from them. How do i go about doing that? I have attached my code below.

angleIncidence = acosd((sind(angleDeclin).*sind(lat - tilt))+(cosd(angleDeclin).*cosd(lat-tilt).*cosd(w)));

if angleIncidence > 90
    angleIncidence = 180 - angleIncidence;
end

I have also tried:

angleIncidence(angleIncidence > 90) = 180 - angleIncidence

Answer 1

[Walter Roberson]

mask = angleIncidence > 90;
angleIncidence(mask) = 180 - angleIncidence(mask);

Answer 2

[Cris LaPierre]

mod(ang+90,180)-90;